The purpose of this test is to investigate the presence of LIN-BUS signals and circuit integrity in relation to systems connected.
LIN-BUS circuit access can be gained at individually controlled components.
As you can see from the example waveform, the LIN bus waveform is a square wave, representing the binary states in a serial data stream. The waveform observed should be free of obvious distortion and noise spikes, and the upper and lower levels should be approximately as in the example (for a 12 V system).
The lower level voltage (logic zero) should be less than 20% of battery voltage (typically 1 V) and the upper level voltage (logic one) should be more than 80% of battery voltage. Note that the voltage levels may change slightly when the engine is started.
We cannot decode the data stream using a scope, so the purpose of this test is to verify that the signal is both present and correct, and is not interrupted by moving the wiring harness or gently tugging the connectors. Faults may be specific to a particular function, such as a non-operating window, or general, where all the functions on the bus are not working. Before condemning a device, use the scope to check that it has power, ground, and a present and correct LIN signal.
Local Interconnect Network (LIN) bus communication is becoming more common on modern CAN Bus-equipped vehicles. It is essentially a low-speed, single-wire serial data bus (a sub-bus of the faster, more complex CAN Bus) used to control low-speed non-safety-critical housekeeping functions on the vehicle, especially windows, mirrors, locks, HVAC units, and electric seats.
The LIN bus is proving popular because of its low cost and also because it reduces the bus load of the supervising CAN network.
We know that our PicoScope users are clever and creative and we’d love to receive your ideas for improvement on this test. Click the Add comment button to leave your feedback.